Thermosetting resins are used in a wide variety of fields, such as electronic materials and optical materials, due to exhibiting excellent heat resistance, chemical resistance, moldability, insulation reliability, and so on. In particular, epoxy resins, which are thermosetting resins, are often used in a variety of applications, but epoxy resins are excellent in terms of the characteristics mentioned above, but are known to be generally hard and poor in terms of flexibility. As a result, epoxy resins can deform or break when subjected to external stress or thermal stress.
Examples of materials that exhibit superior flexibility include silicone resins, urethane resins, thermoplastic resins such as polyethylene, and a variety of rubber materials. Moreover, the flexibility of resin materials requires not only a low elastic modulus and a high tensile elongation, but also requires recoverability following extension when used in a variety of components.
For example, there is ongoing development of flexible display devices, such as electronic paper, which use materials having excellent flexibility. In general, electronic paper uses a system such as an electrophoretic system or a twisting ball system, but these systems are constituted from a laminate consisting of a display layer for realizing a display and an electrically conductive layer for applying a voltage. Electrophoretic flexible display devices use mainly urethane resins (see Patent Document 1). Meanwhile, twisting ball type flexible display devices use silicone resins (see Patent Document 2).
In addition to flexibility, meanwhile, stress relaxation properties are a characteristic that has come to be required of resin materials in recent years. The matter that residual stress increases when an article is deformed as a result of stress being applied means that the force required to return the article to its original shape is large, and this means that if the residual stress is large, detachment and breakage can occur between components. Therefore, excellent stress relaxation properties, that is, reducing the applied stress so as to reduce the residual stress, is considered to be a required characteristic.
However, urethane resins and silicone resins such as those disclosed in the Patent Document 1 and Patent Document 2 exhibit high tensile elongation and excellent recoverability, but are known to exhibit low stress relaxation properties. It is possible to increase the stress relaxation properties of urethane resins by altering the types and combinations of polyols and isocyanates used as raw materials or by decreasing the crosslinking density, but doing so causes the recoverability to deteriorate. In addition, urethane resins have a narrow usable temperature range and exhibit low heat resistance, and therefore have the drawback of being limited in terms of scope of use.
Therefore, display devices produced using these resins have problems such as detachment or breakage readily occurring as a result of residual stress caused by close adhesion to free-form surfaces or by significant deformation. Therefore, it is currently the case that flexible display devices exhibit only limited flexibility.
Other types of rubber material also exhibit such problems, and exhibit high recoverability, but low stress relaxation properties. In addition, other thermoplastic materials such as polyethylene are used in a variety of fields due to being flexible and exhibiting high tensile elongation, but the elastic region of tensile elongation is between a few and several tens of percent, and in the region beyond the yield point, elongation caused by plastic deformation occurs. As a result, thermoplastic materials such as polyethylene exhibit excellent stress relaxation properties, but have the problem of not returning to their original shape following elongation (that is, high residual strain rate).